CCIE notes from experience

CCIE notes from experience

ATM PVCs
For ATM pvc’s, you can either use maps (similar to Frame Relay maps) or
inarp. Inarp will only work with IP, so if IPX is also involved you must use
maps (this may vary with IOS version). Inarp is off by default on a pvc.
Enable it simply by including the inarp keyword in your atm pvc command.
If you do not include it, you must use the map-group and map-list
commands to manually define mappings.

ATM
If you are having trouble with ATM, enable ilmi (atm pvc 2 0 16 ilmi) and
do a show atm ilmi-status. This will show if you are communicating with
the switch.
ATM PVCs
For ATM pvc’s, you can either use maps (similar to Frame Relay maps) or
inarp. Inarp will only work with IP, so if IPX is also involved you must use
maps (this may vary with IOS version). Inarp is off by default on a pvc.
Enable it simply by including the inarp keyword in your atm pvc command.
If you do not include it, you must use the map-group and map-list
commands to manually define mappings.
ATM SVCs
ATM SVCs are still fair game, even without LANE. For this method you
define a pvc for the signaling protocol, qsaal (atm pvc 1 0 5 qsaal), and
optionally one for ilmi (atm pvc 2 0 16 ilmi). However in this case you
have two choices:
You can map (using map-group and map-list) IP or IPX addresses to full,
20-byte ATM addresses. The router then uses qsaal to signal for the ATM
switch to construct an SVC to the ATM address in the map statements.
This is obviously clumsy.
The other alternative is to use ATM ARP Server (IP only?). With this, set
the server using the arp server self command. Then on each client
define the server’s 20-byte ATM NSAP using the atm arp server address
command.
ATM PVC Discovery
This method only uses one PVC – ilmi (atm pvc 2 0 16 ilmi) to discover
VC’s. Use the atm ilmi-pvc-discovery command on the main ATM
interface. This will let the switch announce PVC’s. This also performs ATM
mapping for network layer addresses. This does not require qsaal (atm
pvc 1 0 5 qsaal). It does “stick” them on the main interface – so if you
don’t want them there, write down the VPI/VCI’s, turn off discovery and
configure the PVC(s) on your subinterface. Another alternative is to use
the atm ilmi-pvc-discovery subinterface command. This places the
PVC in the subinterface with the same number as the VPI of the PVC.
BGP
Filtering
To filter routes you can use a neighbor dist-list, just dist-list or a
neighbor route-map with only a match ip address statement. Using just a
dist-list filters them from the routing table but leaves them in the bgp
table. The other two eliminate them from both. An extended access list like
3

access-list 102 permit ip host 10.10.10.0 host 255.255.255.0
seems to work with the first and last option, but not the “plain” dist-list
option…
When filtering based on AS path, using ^ (to denote the beginning of an
AS path) matches the beginning of the path as it is listed in the bgp table.
For example, to match:
Network Next Hop Metric LocPrf Weight Path
* i3.0.0.0 137.39.23.89 1000 50 0 701 80 i
You could use:
sho ip bgp reg ^701_80_
Even though the true “beginning” of the AS path is 80 (that is, the route
was originated from AS 80).
Communities
In order to send communities, you need to enter the neighbor 10.13.13.1
send-community command. This will send any communities the BGP
routes already have to that neighbor. Communities are not sent by default
– they need this command!!!
In order to tag routes with communities, you need:
neighbor 192.168.1.2 send-community
neighbor 192.168.1.2 route-map setcommunity out
route-map setcommunity permit 10
match ip address 2
set community no-export
!
route-map setcommunity permit 20
!
access-list 2 permit 192.168.254.0
You need the second route-map statement to send “all other” routes
without communities. Also, it is helpful to use the global command ip bgp
new-format. Otherwise your communities look really weird!
Synchronization
Turn off whenever possible! With it on, all iBGP learned routes must also
show up in some IGP (OSPF,etc.) Even static routes are not enough!
Aggregate Address
This is a useful command for summarizing an address block. Use the
keyword summary-only to suppress more specific routes. However to
advertise a summary at least one more specific route must be in the
router’s BGP table (via a network command, redistribution, etc.)
4

The summary-only keyword only appears to suppress more specific routes
that are within the natural class defined by the aggregate address and
mask. That is, you can specify an address/mask that is larger than its
natural mask. The exact address/mask you specified will get propagated
via BGP, however it will only suppress more specific routes within its own
natural address class.
Bridging
For bridging over Frame-Relay, there are no special requirements if all
interfaces are point-to-point. However for Frame Relay (or ATM) physical
or multipoint interfaces, you need one frame-relay map bridge dlci
broadcast command for each DLCI that’s part of physical or multipoint
interfaces. However, note that for physical and multipoint interfaces, the
router will not forward packets out the same physical or multipoint
interface that bridge packets were received on (regardless of all else,
including Spanning Tree)!
Spanning Tree
The root bridge is determined by the lowest bridge priority – set by the
global bridge priority command.
On each subnet a designated bridge is elected. This is the bridge that will
have the forwarding path to the root. The bridge with the lowest cost path
to the root will be the designated bridge (and thus will be forwarding). In
the case where two or more bridges have the same path cost to the root,
the bridge with the lowest priority becomes the designated bridge.
The path cost is calculated by adding the “outbound” path costs of all
paths to the root. That is, path costs are added as you are leaving each
router on the way to the root (the path cost as you enter a router is
irrelevant).
All non-root bridges will have exactly one root port. These listen for
BPDUs from the root bridge. Non-root bridges will send BPDUs out all
their designated ports. For all non-root bridges, if a port is not a root port
and not a designated port, it is a blocked port.
Port priority is almost never used. The only time this might be used is if
two non-root bridges had redundant links between them. One of the four
ports for those two links would have to block – port priority would allow
you to control which one it was. If you don’t set this on any of the four, the
IOS will select one to block (but how? Who cares?).
IRB/CRB
5

With CRB for a given protocol (IP or IPX), there will be a group of routed
interfaces and a group of bridged interfaces. The routed interfaces each
get an IP (and IPX) address and can route to any other routed interface –
but not to the group of bridged interfaces. The bridged interfaces can
bridge between each other, but not route to the routed interfaces (the
bridged interfaces don’t even get an IP or IPX address). CRB is not terribly
useful.
With IRB you may have the same set of routed and/or bridged interfaces,
but you can easily establish connectivity between them.
When you configure IRB or CRB you have four choices for each protocol:
1. bridge 1 route ip
bridge 1 bridge ip
Use this to bridge the protocol among interfaces within the bridge
group, but route it to all other interfaces. (Very common). For
interfaces within the IRB bridge-group 1, configure the protocol
information on int bvi1, not on the “real” interfaces.
2. no bridge 1 route ip
bridge 1 bridge ip
Use this to bridge the protocol among interfaces within the bridge
group, but not route it to any interfaces outside of the bridge group.
Do not configure protocol information on int bvi1 or on the “real”
interfaces within the bridge group.
3. bridge 1 route ip
no bridge 1 bridge ip
Use this to route the protocol among all interfaces – within the
bridge group and outside the bridge group. Configure the protocol
information on all the “real” interfaces (within and outside the bridge
group) but not on int bvi1. This is common when you want to
route one protocol (like IP) but bridge another (like IPX).
4. no bridge 1 route ip
no bridge 1 bridge ip
You would probably never use this. This would ‘turn off’ the protocol
for the entire bridge group – you would not bridge it between
interfaces in the bridge group, nor would you route it to any
interfaces outside the bridge group.
Debug
If you need to use debug ip packet [detail] [access-list], remember
that only packets that are processed switched will get debugged. To
disable fast switching (and force process switching) use no ip route-
cache on each interface (especially the incoming interface for the packets
in question).
Dial
My dial strategy is going to be to use the simplest (most dependable)
solution unless directed otherwise. My order of preference for IP will be:
6

1. Floating Static Routes
2. IP OSPF Demand Circuit
3. Dialer Watch
4. Snapshot routing
5. Dial Backup
My order of preference for IPX will be:
1. Floating Static Routes
2. Tunnel IPX through IP (especially effective if using 1, 2 or 3 above)
3. Snapshot routing
4. Dial Backup
The 2503’s and 2504’s typically have an S/T ISDN interface. A 2524 often
will have a U.
Floating Static Routes
For IPX to use a static, default route, the WAN (i.e., ISDN) must use
IPXWAN! IPXWAN needs an internal-network number first!
SnapShot Routing
Remember, snapshot routing only works with RIP (IP), IGRP (IP), RIP and
SAP (IPX).
Even with Snapshot routing you still need the same old dialer map
statements that you always have (typically)…plus one or more for
snapshot.
PPP Authentication
You want to indicate ppp authentication chap under the physical
interface (dialer maps) or the physical and logical interface (dialer
profiles). If you don’t want one side to use chap (if you don’t want that
router to challenge the other) omit the ppp authentication chap. However
if the opposite router has ppp authentication chap, you must have the
other router’s name & password in your database.
For PAP authentication, you need the same config as with CHAP, yet also
the receiving router seems to also need a ppp pap username r4 password
0 cisco, where r4 is that router’s own hostname and cisco is the
password.
Distribute Lists
* Try adding the word log at the end of an access-list statement to log
what is happening with the access list.
7

Distribute lists “in” block routes from the routing table, but not the (OSPF
or other) database. This will block the routes from appearing in that router,
but not in other routers that run (OSPF or other) and get the same Link
State Database.
Distribute lists “out” are typically much more effective from blocking a
route from a large portion of the network. However with OSPF
distribute-list out only works on External Type 1 or 2 routes – not with
internal OSPF routes.
Distribution lists may not take effect immediately. You may have to bounce
the interface or do a clear ip route * to activate them.
The distribute-list list# out process is very tricky. For example:
2501b(config)# router ospf 103
2501b(config-router)#distribute-list 16 out eigrp 1
It would appear that this would regulate what ospf sends out to eigrp 1.
But instead it controls what OSPF receives in from EIGRP 1 (or, more
aptly, what EIGRP sends out to OSPF).
DLSw
Here is a brief overview of the types of DLSw transports:
DLSw also uses noncanonical (T.R.) format for mac addresses.
DLSw will automatically convert between Ethernet and Token Ring
stations if they are located on different routers. In order to get Ethernet
and Token Ring stations to communicate on the same router, SR-
Translational bridging must be enabled.
TCP – probably the most robust DLSw implementation – recommended.
FST – does not perform local acknowledgement, supports Token Ring
only, fewer queuing options.
Direct – supports HDLC and Frame-Relay only, fewer queuing options (No
IP encapsulation).
LLC2 (lite) – less overhead but also less rerouting, Frame-Relay only.
DLSw chooses 1 path by default, but can be configured to use multiple
paths.
DLSw can choose paths based on cost. Cost in a local-peer statement is
what is advertised out to all remote peers. Cost in a remote-peer
statement sets the cost to connect to that peer.
8

DLSw can limit the MTU size (handy going from TR to Eth) using the lf
1500 keyword and value on the remote-peer statement.
Filtering
With dlsw prom-peer-defaults and dlsw peer-on-demand-defaults all
filters (dmac-output-list, host-netbios-out, lsap-output-list, etc.) are
outbound to other peers (not outbound to the LAN interface).
With dlsw remote-peer statements all filters (dmac-output-list, host-
netbios-out, lsap-output-list, etc.) are outbound to other peers (not
outbound to the LAN interface).
A local DLSw peer can specify dlsw remote-peer 1 tcp 10.10.10.10.
This command refers to list 1. It can be port list 1, ring list 1 and/or bgroup
list 1. This command limits what the remote peer (in this case 10.10.10.10)
can access locally (on the peer on which it is defined).
Border Peers/Peer Groups
By default for DLSw to have “full mesh” connectivity, you need a full mesh
of DLSw connections. The exception is peer groups. With peer groups you
can group DLSw routers into groups. Within a group each router only
needs a connection to the bordrer peer(s). The border peer forwards
broadcasts to all other peers within the group as well as any other border
peers (from different groups) that are configured (basically acting like a
BGP route reflector). Once the explorer finds its destination, a connection
is setup router router (listed in the routers as peer-on-demand, or
simply pod), even if the routers are in different groups.
Usually in this case use promiscuous peering. That is, all routers will likely
need to be configured to accept any connection (promiscuous) since they
could be getting connections from many routers.
Note: in the above scenario you will get promiscuous peers and pod (peer
on demand) peers. To filter these use dlsw prom-peer-defaults and dlsw
peer-on-demand-defaults to filter! Remember – these filters are
outbound to other peers!
TCP connections
DLSw sets up connection on TCP ports 2065 and 2067. DLSw allows for a
TCP connection to be built using one of these ports (likely 2065) in each
direction. However if the DLSw routers can accommodate only one bi-
directional connection (this will almost always be the case for Cisco
routers), one TCP connection gets torn down. The router with the higher
DLSw peer IP Address tears down the connection. Watch this if you have
to NAT a DLSw peer address! Also its best to allow TCP 2065/2067 both
ways through an access-list, even if the “steady state” DLSw coinnection
will only require it in one direction.
9

EIGRP
If you have to run EIGRP over a dial interface, I recommend using dialer
watch-group.
For NBMA topologies (Frame-Relay, ATM) EIGRP can have split-horizon
disabled for spoke-spoke reachability (true for both IP and IPX).
Frame Relay
If you see a PVC with the status of “deleted,” it probably means you typed
in an interface-dlci 100 command, but the frame switch is not
announcing (and doesn’t know about) that DLCI – check DLCI.
If you see a PVC with the status of “inactive,” it probably means the local
router’s connection to the frame switch is fine, but there is a problem with
the ‘far’ end of the PVC. Check the router that is supposed to terminate
the PVC.
If you use a frame-relay map statements, you don’t need frame-relay
interface-dlci command(s) (unless you need to do traffic shaping). It
may be a good idea to only use the map statements.
In Frame Relay you may want to place a map statement for your own IP
address so that you can ping it (or ask the proctor if this is necessary).
Inverse Arp and Mapping
Frame Relay needs a way to connect, or map, a Layer 3 address (IP or
IPX address) with a particular Frame Relay DLCI. That is, when a router
attempts to forward packets to an IP or IPX address it needs to know out
which virtual circuit – specified by a Frame Relay DLCI – the packet
should be forwarded.
In some cases (such as where two routers are connected by a single
virtual circuit, i.e., a single DLCI) the routers can use inverse-arp to
determine the Layer 3 (IP or IPX) address at the opposite end of the
virtual circuit. However in other cases, such as two “spoke” Frame Relay
sites connected by one “hub” Frame Relay site, the two spoke can not use
inverse-arp to learn each other’s Layer 3 addresses. This is because
inverse-arp packets are never forwarded (in this example, they are not
forwarded by the “hub” router).
In these cases it is common to manually map (define) each Layer 3
address the router can reach to a specific DLCI (virtual circuit). Using sub-
interfaces is an easy way to avoid doing this, but when does the CCIE
exam ever take the easy way?
10

Also, if you perform mapping on a router, it is best to map every router,
including the hub router. Even if connectivity exists between that router
and the hub router, if you are mapping other remotes make a habit of
mapping the hub router as well. In some version of IOS inverse-arp is
disabled once a Frame Relay mapping occurs, however the problem this
poses is often not apparent until the next reboot.
The way this can occur is as follows: suppose router A is a “spoke” router
connecting to router B. Router C is also a spoke router that connects to
router B. Router A uses inverse-arp to map router B’s IP address to a
particular DLCI. However router A can not inverse-arp for router C’s IP
address as discussed. A map statement is placed in router A for router C.
Everything works great since you router A has the two mappings it needs:
a dynamically learned one for router B (via inverse-arp) and a manually
learned one (via a map statement) for router C.
However with some versions of code the map statement disables inverse-
arp. Thus once the router is rebooted is loses its dynamically learned
mapping for router B. Since the map statement has disabled inverse-arp,
connectivity is lost. Thus, to be safe if you are performing map statements.
add one for each router in the Frame cloud.
11

OSPF
A Frame Relay interface (not a subinterface) defaults to OSPF network
type of nonbroadcast (NBMA). If using the default non-broadcast network
type, be sure to set ip ospf priority 0 on all remotes.
A Frame Relay point-to-point subinterface defaults to OSPF network type
of point_to_point.
A Frame Relay multipoint subinterface defaults to OSPF network type of
nonbroadcast (NBMA).
If you use point-to-point subinterfaces at one end of a PVC and no
subinterfaces at the end, you must account for the type mismatch. For
example, use ip ospf network point-to-point at the end not using
subinterfaces. If you use a combination of physical and multipoint
subinterfaces, use ip ospf network point-to-multipoint.
If you can’t use broadcasts (as with the frame relay map statements or if
you must use ip ospf network point-to-multipoint non-broadcast, for
example) you must manually define OSPF neighbors with the neighbor
statement.
Getting Started Checklist
It is easy to gather enough information about the lab to be able to prepare
a “getting started” checklist. This is a list of the first steps to take on the
morning of the first day of the lab. Here is my list, in order:
1. Read the lab exam twice. Yes, twice. Don’t skim it and read it –
read it twice. Make a list of:
a. Hidden issues and pitfalls
b. Your strong and weak areas
2. In between the first and second readings, configure the terminal
server to connect to every router and switch in your rack. Make r1
the first connection, r2 the second connection, etc. Make the
switches the last connections.
3. Check and record the IOS version, IOS image (name – feature set)
and interfaces on each router.
4. Unless they are in the initial configuration script, write erase &
reload each router. This will assure a clean start. It will also verify
that they will reload properly – you don’t want to discover they have
a problem rebooting at 3:30! If you do this in between readings, the
routers will have plenty of time to reload.
5. Create an IP address matrix. Don’t waste time making something
that can be hung at the Museum of Fine Arts when you’re through.
Just make a very simple line for each major network. Create major
13

divisions – 64, 128, 192, etc. Write down each address that is
required and each one that you select.
6. Begin cabling the routers per the lab.
7. In notepad enter all commands that will be entered into every
router.
8. Configure the routers with the above commands as well as all
“layer 2” commands. Verify:
a. Show isdn status yields “MULTIPLE_FRAME_ESTABLISHED”
b. Verify all interfaces are up, up
c. Verify all Frame-Relay PVCs are LOCAL and ACTIVE
IGRP
When changing the distance on IGRP you should perform a clear ip
route. Otherwise IGRP seems to wait until the routes clear naturally
(holddown, etc.) before they are reinstalled with the new distance.
IGRP does not exchange the default route (0.0.0.0) as most of the other
protocols do. If you must have a default route with a router running IGRP,
use:
ip default-network 172.16.0.0
where 172.16.0.0 is a classful network. This classful network (not a
subnet) must be in your routing table. It also must be part of the IGRP
process (either via the network statement or redistribution). This will cause
this router to generate a candidate default route via IGRP.
Remember, IGRP has a lower admin distance than OSPF. That’s probably
not what you want!!
IKE
IKE is the Internet Key Exchange standard and is usually performed using
the ISAKMP protocol. IKE is often used with IPSec because it automates
key management and controls the security associations that are formed,
though IKE is not required for IPSec. IKE policies define five things:
• encryption algorithm (such as des)
• hash algorithm (such as sha or md5)
• authentication method (such as rsa-sig, rsa-encr or pre-share)
• Diffe-Hellman group (such as group-1 (768-bit) or group-2 (1024
bit))
• security association lifetime (in seconds)
All of these have defaults (and the defaults can be used) except
authentication – that must be specified. Pre-share is by far the easiest
authentication method. Rsa-sig authentication requires a certificate
authority (and thus is very unlikely to be on the CCIE Lab). These
parameters affect the data that flows between hosts during the IKE
14

negotiation – not the actual data flows. Encryption and authentication of
data flows is defined by the transform set in IPSec.
IPSec
To configure IPSec:
• Determine whether to use ISAKMP (recommended) or manual
config for security associations
• Configure ISAKMP (recommended) or manual IPSec
Then:
1. Define the ISAKMP policy (ISAKMP only)
2. Define the keys (pre-shared, RSA, etc.)
3. Define a transform set (security configuration)
4. Define an access list to determine what traffic will be sent via IPSec
5. Create crypto map entries
6. Apply the crypto map to an interface
It appears IPSec likes to have the crypto map applied to the “outer most”
interface. In the past I have applied the crypto map statement to the LAN
(inside) interfaces and had no success (even if the routers are IPSec
peering between loopbacks).
Access lists
For ipsec-manual mode (not using IKE/ISAKMP), only 1 access list entry
is permitted; all others are ignored.
Always make access lists mirror images of each other at opposite ends!
Don’t use the any keyword in your access lists.
IPSec through a Tunnel Interface
For running IPSec through a tunnel, first define the tunnel between the two
physical interfaces on each router. Once the tunnel is working, define the
IPSec peers between loopback interfaces. To do this you will need the
crypto map mymap local-address loopback 0 command (to set the peer’s
local IPSec peer address).
You will need some routing so that each router knows of the other’s
loopback address – static routing, a routing protocol through the tunnel,
etc.
Enable the crypto map on both the physical interface and the tunnel
interface.
IPX
15

When enabling IPX routing globally, use ipx routing x.x.x where
x=router number. Thus, router 1 would be ipx routing 1.1.1 (easier for
access lists, IPX pings, etc.)
When you apply ipx routing 1.1.1 to a router, it applies that “host”
address to all non-LAN interfaces (serial, ISDN and loopback interfaces).
The internal network always uses 0000.0000.0001, and the LANs use the
“natural” mac address.
An IPX router will not install a SAP for which the network for that SAP was
learned upon a different interface. Watch this on distribute lists.
When you enable ipx router eigrp, rip will stay on for those eigrp interfaces
until you turn it off with the no network ### under ipx router rip. When
nlsp is enabled on an interface, rip packets will only be sent if the other
side is also sending rip packets – which is unlikely. RIP and SAP may be
manually turned off with the no ipx nlsp rip and no ipx nlsp sap
commands.
Filtering
Use distribute lists on a routing process – rip, eigrp or nlsp. If you do not
specify an interface for the distribute list, the list gets applied to all
interfaces.
For:
ipx router rip
distribute-list 800 out eigrp 1
It would appear that this would regulate what RIP sends out to EIGRP 1.
But instead it controls what RIP receives in from EIGRP 1 (or, more aptly,
what EIGRP 1 sends out to RIP). [Acts same as IP]
For SAP filtering, use distribute-sap-list under the appropriate ipx
router command. This lets you specify the source network (with mask),
any source network, source network and host, service type (i.e. 4=file
server), server name. Acts just like the distribute-list for routing updates.
The ipx router-filter interface command allows you to specify routers
from which you will or will not accept updates – however it only works for
RIP and EIGRP (not NLSP). With this command you can specify exact
N.H.H.H routers or just permit/deny any router from a given network by
only listing the network.
You can filter input (received updates) or output (sent updates) networks
or SAPs on an interface level with one of the following commands:
ipx input-network-filter
ipx input-sap-filter
16

ipx output-network-filter
ipx output-sap-filter
Useful things to know for extended filters:
IPX Protocol (also called “packet type”) is similar to IP protocol (TCP,
UDP, GRE, etc.) Usually set this to “any” in filters.
IPX RIP uses socket number 453.
IPX SAP uses number 452.
File servers use server-type 4 (in SAPs)
Print servers use server-type 7 (in SAPs)
EIGRP
Split Horizon may be disabled when using IPX EIGRP with the no ipx
split-horizon eigrp 1 command. This is handy on the hub router of
Frame-Relay or ATM networks.
To use just EIGRP (and not RIP/SAP) on a WAN link, use the network
xxx command under IPX router eigrp 1 and the no network xxx under
the IPX router rip. On WANs this will enable SAPs automatically. On
LANs this will enable routing updates, but not SAPs. To enable EIGRP to
propagate SAPs on LANs, use ipx sap-incremental eigrp 1.
Redistribution
RIP NLSP automatic
RIP EIGRP automatic
EIGRP NLSP not automatic, must be specified
Connected EIGRP automatic (!!)
In any case it can be controlled via an access list. When using an ACL to
control redistribution, deny means deny explicit routes – only aggregates!
Permit means permit explicit routes.
NLSP NLSP (with different area tags):
• Not automatic, use “route-aggregation” command
• When aggregation is turned on, its by area address
• It seems to advertise the area summary, but also explicit routes. To
prevent explicit, use the redistribute access-list command.
NLSP
When configuring NLSP with multiple areas, use a tag, such as area1 or
area2. Use it both in the global ipx router nlsp area1 command as well
as the interface ipx nlsp area1 enable command.
ISIS
17

Two ISIS nodes with the same area address will exist in the same area.
This will allow them to establish a Level 1 relationship. ISIS with different
area addresses will exist in different areas and establish a Level 2
relationship. By default ISIS routers can be level 1/2 routers, though this
can be manually defined globally (is-type) or on each circuit (isis
circuit-type).
It appears only the first 4 characters in an ISIS address denote the area.
For example, the address 49.2222.0000.0000.5555 should have an area
address of 49.22. However for simplicity make all 4 digits in the first group
of four the same (and equal to the area address – 49.2222, for example).
Make the last four characters (5555, for example) all the same (as
opposed to “0005”). This represents ‘router5’ or ‘r5’.
ISIS uses two different network types and they cannot be changed.
Frame-Relay physical and multipoint interfaces are one type; point-to-
point interfaces are the other type. These must match for adjacencies to
form. If no adjacencies are forming use the debug isis adj command.
The only other alternative is to create a tunnel.
An ISIS interface does not get its own address. It uses the NET of the
router to which it connects. However it does get its own circuit ID. The
circuit ID is the router’s NET with the selector byte (last byte) incremented.
show clns neighbor
show clns interface
debug isis adj
Multicast
IGMP/CGMP
IGMP (Internet Group Management Protocol) is the standard multicast
protocol that controls hosts joining multicast groups (and thus determines
where a router needs to forward multicast traffic). CGMP is Cisco’s
proprietary IGMP. It only goes between the router and the switch, telling
the switch on what ports it needs to forward multicast traffic.
PIM
PIM (Protocol Independent Multicast) is one of the leading multicast
standards. PIM can operate in sparse mode, dense mode or sparse-dense
mode.
In dense mode, multicast routers assume all other multicast routers want
multicast flows. If a multicast router has no clients for a flow, it can send a
Prune message back toward the source to stop that flow.
18

In sparse mode, multicast routers assume all other multicast routers do
not want multicast flows. A multicast router must specifically request a flow
(based on the requests of its clients). Mutlicast routers and multicast
sources are tracked by a rendezvous point (RP).
In sparse-dense mode the interface acts either like sparse mode or dense
mode for each multicast group. Thus an interface can be in sparse mode
for some groups and dense mode for other groups.
DVMRP
DVMRP (Distance Vector Multicast Routing Protocol) is not fully supported
by Cisco. However Cisco can send and receive packets from a DVMRP
router.
NTP
For basic NTP configs, see Rob’s Study Sheet. On the “master” or
“server” router to control what routers can access NTP:
ntp access-group serve 71
Where 71 is the ACL that restricts what routers can use NTP and where
serve is…
To use authentication with NTP, use:
OSPF
If you have a partial mesh Frame-Relay network (likely) and you are
forced to use the non-broadcast network type (as opposed to the more
favorable point-to-multipoint type) you will likely have to manually
configure neighbors. In this case you will probably only need to define
these at the hub router. Use ip ospf priority 0 at the remotes.
You don’t need no auto-summary.
Loopback networks won’t be part of the OSPF process by default – they
need to be added with the network statement. Loopback networks get
defined as host routes (/32 mask) regardless of the “real” mask. However
if you want the “whole loopback subnet” to be visible to the rest of the
network, consider:
• Placing the loopback in its own area and summarizing:
interface loopback0
ip address 192.168.253.1 255.255.255.0
router ospf 1
network 192.168.253.0 0.0.0.255 area 4
area 4 range 192.168.253.0 255.255.255.0
19

• Defining the ospf network type as point-to-point (V12.0 and later)
interface loopback0
ip address 192.168.253.1 255.255.255.0
ip ospf network point-to-point
Network Types
In Frame Relay you typically need frame-relay map statements if using no
subinterfaces (just the physical interface) or point-to-multipoint
subinterfaces on the remotes (in a partial mesh topology).
This is even true if you use the default OSPF network types for these
interfaces, non-broadcast (NBMA). However if you use ip ospf network
point-to-multipoint, you do not need frame-relay map statements (at
least for IP) – even at the remotes. This is because this network type
makes the Frame Relay partial mesh look like a collection of point-to-point
networks.
In a hub-and-spoke frame relay network, if the hub is using a point-to-
multipoint subinterface, either ip ospf network point-to-multipoint is
required or manually defining neighbors at the hub is required. This is true
in 11.3, though it seems to have been removed in 12.0.
Distance
You can set distances for intra-area, inter-area and external OSPF routes
with the distance ospf router command. This can control what routes the
router chooses to place in the routing table.
Summarization
When you use an area 1 range command it will summarize all OSPF
internal routes, but none of the OSPF external (type 1 or 2) routes.
When you use the summary-address 172.17.0.0 255.255.0.0 command,
it does the opposite: it summarizes all OSPF external routes but none of
the internal OSPF routes. It also only works on routers that are the ASBR
for the external routes being summarized. Also, the summary
advertisement seems to be an external type 2 route, with the metric being
the lowest of the routes within that range.
However the OSPF summary-address command can also summarize
external (type 1 or type 2) OSPF routes that are being redistributed into
another protocol from OSPF. This can be very useful for IGRP and RIP,
which are bound by FLSM. For example, OSPF can use the summary-
address command to summarize many /27 OSPF networks into a single
/24 to advertise into the IGRP domain which uses a /24 mask. This
command is entered on the ASBR between the OSPF and the IGRP (or
20